Solar Pro 2 is a 31-billion parameter large language model developed by Upstage AI. Released in July 2025, it serves as the successor to the original Solar Pro architecture, featuring a significant parameter increase and enhanced efficiency. The model is built with a unique hybrid architecture that allows users to toggle between Chat Mode—designed for fast, non-reasoning, and direct conversational tasks—and Reasoning Mode, which utilizes chain-of-thought (CoT) processing for complex logical steps.
The non-reasoning or "Chat Mode" of Solar Pro 2 is optimized for low-latency interactions and high throughput. It is particularly effective for real-world agentic workflows, document processing, and general-purpose natural language tasks. The model introduced a refined tokenization algorithm that significantly reduces token overhead, improving cost-effectiveness and speed, especially for Korean and document-heavy workloads.
Technically, Solar Pro 2 features a 64K (65,536) token context window, doubling the capacity of its predecessor. It has demonstrated frontier-level capabilities in multilingual benchmarks, showing high proficiency in Korean, English, and Japanese. Despite its compact size of 31B parameters, it has been recognized for delivering performance comparable to much larger proprietary models in general knowledge and instruction-following tasks.